One-way torque-transmitting mechanisms or Mechanical Diodes generally are sprag, roller, or strut type and are designed to prevent overrunning between two members in one direction of operation while permitting overrunning of a member in the opposite direction. These devices might either be torque-transmitting mechanisms of the rotating type or torque-transmitting mechanisms providing a stationary operation such as a brake. These one-way devices have found a lot of use in power transmission situations wherein it is desirable to establish at least one ratio such that on a ratio interchange, the one-way device will simply overrun permitting a change within the gearing of a power transmission.
More recently, it has been proposed that the friction devices of a power transmission be actuated by torque-to-thrust mechanisms. Types of torque-to-thrust torque-transmitting apparatus or mechanisms are shown in U.S. Ser. No. 10/303,245 filed Nov. 25, 2002 and now U.S. Pat. No. 6,874,609; U.S. Ser. No. 10/319,957 filed Dec. 16, 2002; U.S. Ser. No. 10/738,564 filed Dec. 17, 2003 and now U.S. Pat. No. 6,948,396 and U.S. Ser. No. 10/946,759 filed Sep. 22, 2004. Each of these patent applications is assigned to the assignee of the present
In a torque-to-thrust apparatus in an automatic transmission application, an electric motor is generally employed to provide input rotation through a rotary member, which is operatively connected with a linear thrust member through a cam arrangement such that upon rotation of the electric motor the linear member will provide an apply force to a friction torque-transmitting mechanism such as a clutch or brake. In order to retain the clutch or brake engaged, the electric motor must remain energized or a significant friction must be built into the torque-to-thrust apparatus.
The present invention seeks to improve the torque-to-thrust apparatus by providing a mechanism for retaining the engagement of the torque-transmitting mechanism but with little friction on the apply stroke which determines the required motor size.